Northern Ireland is heading for a snap election after Sinn Fein triggered the implosion of the powersharing executive by declining to re-nominate a deputy first minister.

Barring a highly unlikely u-turn by the republican party, the institutions will now fall at 5pm on Monday and Northern Ireland Secretary James Brokenshire will be legally obliged to call the election.

At the start of Assembly business on Monday, Sinn Fein refused to replace Martin McGuinness as deputy first minister, a week after he quit citing irreconcilable differences with his long term Democratic Unionist partners in government.

His resignation was precipitated by the renewable heat incentive (RHI) scandal - a botched eco-scheme set to cost Stormont £490 million - but that row has also reignited a range of other bitter disputes dividing the coalition.

Sinn Fein MLA Michelle O'Neill told the Assembly: "The DUP have treated these institutions and sections of the community with contempt and arrogance."

The Prime Minister's official spokeswoman said Mrs May wanted to make sure Northern Ireland has "a voice" in the run-up to the start of EU withdrawal talks - expected to be triggered by the end of March with the invocation of Article 50 of the European Union treaties.

The Stormont Assembly will limp on until it is formally dissolved. An election is likely in late February or early March.

The failed reappointment process came at the opening of a full day of Assembly business during which a number of elements of the political crisis will be debated.

Emergency proposals aimed at reducing the RHI overspend are being proposed by DUP economy minister Simon Hamilton while Sinn Fein will also table a motion of no confidence in DUP speaker Mr Newton.